The present invention relates to a method of producing a polymer insulator, which comprises a core, an overcoat member arranged on the core, and a fitting member for securing the core at its both ends, and, wherein the core and the fitting member are secured under pressure at both ends of the core by contacting a ring-shaped protrusion portion arranged at both ends of the overcoat member to an open inner end of the fitting member. The invention also relates to an end processing apparatus utilized for this producing method.
Usually, as shown in FIG. 4, a polymer insulator 51 used for electric power transmission and distribution comprises an FRP core 52, an overcoat member 53 arranged on the FRP core 52, and a fitting member 54 for securing the FRP core 52 and the overcoat member 53 at both ends. In the polymer insulator 51 having the construction mentioned above, there is the possibility that the polymer insulator 51 may be broken or lose its function due to the following reasons:
(1) Fitting strength is decreased due to an erosion of the fitting member 54;
(2) Cracking occurs at the overcoat member 53 and the FRP core 52, so that an electric insulation defect is generated; and
(3) As a worst case, a brittle fracture of the FRP core 52 occurs since an alkali component is eluted into a glass component in the FRP core 52 to which stress is applied.
Therefore, water intrusion into the fitting member 54 must be prevented.
In order to achieve a complete water proof condition between the fitting member 54 and the overcoat member 53, a ring-shaped protrusion portion 55 is arranged at both ends of the overcoat member 53 and a portion having the protrusion portion 55 is secured to the fitting member, so that the protrusion portion 55 serves as an O-ring. This method is disclosed in Japanese Patent Publication No. 2664616, and it achieves satisfactory results. In this method, in order to obtain such a water proof condition by contacting under pressure the protrusion portion 55 and the fitting member 54, an inner diameter of the fitting member is adjusted suitably and the thus obtained fitting member may be connected to the protrusion portion 55.
In the polymer insulator 51 wherein the protrusion portion 55 is arranged at the end of the overcoat member 53, the overcoat member 53 is formed around the FRP core 52 by using a metal mold. Therefore, it is not possible to vary the position of the protrusion portion 55 formed integrally with the overcoat member 53 once it is formed. As a result, there arises a problem wherein the shape and the number of the protrusion portion 55 to be formed cannot be substantially varied. Moreover, when a polymer insulator having a little shorter length is to be obtained by reducing the number of sheds of the polymer insulator 51, it is necessary to change the metal mold and therein arises a problem as such a metal mold change requires a considerable amount of time. Further, it is impossible to re-create a polymer insulator having a little shorter length by reducing the number of sheds of the ready-made polymer insulator. Therefore, it is difficult to effectively process a small-lot order, and productivity decreases if such a small-lot order is undertaken.
An object of the invention is to eliminate the drawbacks mentioned above and to provide a method of producing a polymer insulator and to provide an end processing apparatus utilized for this method, wherein the shape and number of protrusion portions to be formed can be varied without changing the metal mold, and, wherein a product having a suitable length can be obtained by varying the number of sheds of a ready-made formed body.
According to the invention, a method is provided for producing a polymer insulator having a core, an overcoat member arranged on the core, and a fitting member for securing the core at both ends. The core and the fitting member are secured under pressure at both ends of the core by contacting a ring-shaped protrusion portion arranged at both ends of the overcoat member to an open inner end of the fitting member. The method comprises the steps of forming the overcoat member on the core; forming the ring-shaped protrusion portion integrally with the overcoat member by processing an end portion of the overcoat member, and securing the fitting member.
Moreover, an end processing apparatus utilized for the method of producing the polymer insulator mentioned above, comprises a core holder for holding a core, a rotation drive device arranged rotatably around the core holder at a center of a central axis of the core, and a whetstone having a shape for forming an end portion of an overcoat member of the polymer insulator. The whetstone is arranged to the rotation drive device rotatably around its center axis, wherein the whetstone itself is rotated and the rotated whetstone is rotated around the end portion of the overcoat member on the core held by the core holder, so that a protrusion portion is formed integrally with the end portion.
In the method of producing the polymer insulator according to the invention, the ring-shaped protrusion portion is formed integrally with the overcoat member by processing the end portion of the overcoat member. Therefore, it is possible to easily vary the shape and number of protrusion portions to be formed. Moreover, as a preferred embodiment, the producing method further includes the steps of cutting the overcoat member of the polymer insulator to a predetermined length, and processing an end portion of the thus cut overcoat member so that the ring-shaped protrusion portion and the overcoat member are integrally formed. In this case, it is possible to obtain the polymer insulator having a predetermined length from the ready-made or stocked polymer insulator. Therefore, according to the method and apparatus of the invention, it is possible to effectively process a small-lot order and to increase productivity by reducing the number of metal mold changing operations. In addition, the ring-shaped protrusion portion can be formed to the end portion of the overcoat member on the basis of the center of the core. Therefore, it is possible to obtain the ring-shaped protrusion portion which can achieve better securing, even if the overcoat member is eccentric at the processing position.